Borderline Personality Disorder (BPD) is a prevalent and enduring psychiatric disorder found in approximately 2% of the population and 20% of hospitalized psychiatric patients. It is characterized by great volatility, impulsivity, sucidality, and unstable interpersonal relationships, and has proved difficult to treat. Suicide rates of approximately 10% have been reported in borderline patients. A core underlying feature of BPD is extreme emotional instability and this has been shown to be associated with the suicide threats, gestures and acts, inappropriate anger, and identity disturbances which prove so dangerous and disruptive for these patients. Despite its central role in the pathology of BPD, emotional instability is not well understood. This study employs functional magnetic resonance imaging (fMRI) to identify the disturbances in brain emotion processing systems that may explain the impairments in emtional control in BPD. It looks in particular at regional brain activity when BPD patients are consciously trying to control their emotional reactions to disturbing images and as they are systematically re-exposed to these images. Identification of the patterns of brain activity that are associated with efforts at conscious emotional control or with habituation to repeated exposure can lead to the development of new pharmacological approaches to treatment, to the development of new and more appropriately targeted cognitive/behavoral psychotherapeutic strategies, and the identification of brain activity markers for BPD that may guide future genetic studies. To achieve these objectives, we will obtain fMRI images of 30 BPD patients, and of comparison groups of 30 non-borderline personality disorder patients (i.e. patients with Avoidant Personality Disorder) and 30 healthy volunteers 1) as they make efforts to control their emotional reactions to emotion- inducing pictures and 2) as they are exposed to repeated presentions of the same pictures. The findings of this study may help in the development of new treatment strategies for BPD, a disorder which has not only great emotional costs in terms of the suffering experienced by borderline patients and their loved ones, but also social costs since BPD patients typically function at a level substantially below that of individuals with comparable intellect and they consume a disproportionate share of metal health resources. A more effective treatment for this disorder would thus greatly benefit public health.